Circuit breaker with temperature compensation



Dec. 6, 1949.. w. a. STILWELL m 1 CIRCUIT BREAKER IITH TEIPERATURE GOHPENSATIOH Filed Jan. 8, 1944 .1 Y I Mm TTO EY Patented'Dec. 6, 1949 UNITED STATES PATENT OFFICE CIRCUIT BREAKER WITH TEMPERATURE COMPENSATION William E. Stilweil. Jr., Cincinnati, Ohio, alaignor a corporation of New York to John B. Pierce Foundation, New York, N. Y

Application January 8, 1944, Serial No. 517,488

of collar formation, and as appears in Fig. 1, said ring cooperates with a shoulder 25 formed ,in the wall of the casing II, to provide a groove ,for the reception of the ring 24 and the retention by the ring 24 of the rim of a snap spring 26; the spring 28 is secured at its central hub to a monmagnetlc armature shaft 21, as by a stud and nut, as shown.

The armature shaft 28 is connected similarly It is an object of the invention to provide 10 at its one end to the armature 2| and at its other temperature compensation for overload protective electric circuit breakers.

It is an object of the invention to provide an electric circuit breaker embodying a movable end to the central hub of the contact member 29. The contact member 29 is provided with contacts 20, IO, secured at diametrically opposite locations on the rim portion of the contact member 29, as

contact consisting of a bimetallic snap spring 16 is illustrated in Fig. 2. The contact member 29 which serves to throw from closed circuit to open circuit status under the heating effect of an overload condition.

It is an object of the invention to provide an electric circuit breaker embodying means for adjusting the tension in a bimetallic movable contact according to outside temperature conditions, whereby the heating or cooling effect of such outside temperature does not materially affect the calibration of the movable contact for operation under predetermined overload conditions.

Further features and objects of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which:

Fig. 1. is a sectional elevation of a preferred embodiment of circuit breaker embodying the present invention, a remote control circuit therefor being schematically shown; and

Fig. 2 is a plan view of the movable contact element of said circuit breaker.

Referring tothe drawings, a preferred embodiment of the invention includes a housing l0, preferably a tubular structure of insulation material, one end of which is closed by an insulating block ll.

Contacts l2, l2 fixed in said block are for connection with'the load circuit to be controlled.

Solenoid coils H, i5 are interconnected for selective operation in a circuit which includes a momentary contact switch S, as schematically shown in Fig. 1.

Said solenoid coils are disposed within metallic, preferably iron, shells II, "a, and i1, Ila secured in any suitable manner within the casing i0. Said shells collectively provide opposed pole pieces I8 and I9, and a cylindrical chamber 2. within which is slidably contained a soft iron armature 2 I.

Shell I1 is shown resting upon a ring 24, i. e.,

a Movable contact member 29 and spring 26 are each preferably of the type of snap springs disclosed and claimed in my presently co-pending application Serial No. 441,382, now abandoned, filed May 1, 1942, entitled Toggle springs, and its 5 continuation and substitute application Serial No. 628,447, filed November 14, 1945, and like entitled. A characteristic of such snap spring is that an application of force to the hub of the spring, over a distance of less than half of the total throw of the spring, is sufficient to cause the spring to complete its throw by reason of certain reactive forces created within the spring itself. For this reason, the respective solenoid coils I4, i 5, are required to be energized for but a short time, since the resulting movement of the armature 2| in one or the other direction is sufficient to initiate the throw of the snap spring 26, whereupon the reactive forces within the snap spring continue the throw of the armature and rod assembly to final stage.

The movable contact member 29, and the snap spring 20 are each of the shape disclosed in Fig. 2 with respect to the contact member 29. Each has a double equilibrium point, in that each will remain in the convex or concave position to which it is snapped. Each is bimetallic, and under the influence of temperature change, will assume a greater or less curvature in advance of its inversion.

Movable contact member 29 is calibrated to invert from its normally concave position to a convex, i. e., open circuit position when its temperature, resulting from the heating effect of the load circuit passing therethrough, attains a predetermined limit. The contact member 29 then assumes,

3 and retains, the position indicated by the dash lines of Fig. 1, withthe contacts 96 out of circuit closing position and in close adjacency with the solenoid shell l6.

A characteristic of the present invention is its compensation for temperature change of the atmosphere surrounding the case It. For example, an aircraft in which the circuit breaker is used may be subjected to a temperature on the ground to over one hundred degrees, and shortly after the take-oil, may be in below-zero substratosphere temperatures.

The movable contact 29 is bimetallic and so arranged that an increase of its temperature will cause it to invert and throw to open circuit position. Therefore, a lowering of its temperature will require a greater amount of current passing therethrough to cause it to attain the temperature necessary to perform its normal function of snapping to open circuit position. Conversely, if the contact 29 were heated due to the radiated temperature of the case III, a less amount of overload current would bring about its transition from closed circuit to open circuit position. To compensate for this, and to insure that the contact 29 inverts within .a relatively close range of overload condition, the bimetallic snap spring 26 is so arranged that at a low temperature, assuming the circuit breaker to be in closed status,

the spring 26 will become more convex and will move the armature and rod assembly upwardly the fixed contacts l2 with greater pressure to increase the internal stresses in contact", will supplement the stresses engendered therein by the heating of the contact under overload. Therefore, when the predetermined overload condition is attained in the load circuit, the combination of the temperature increase resulting from the overload and the increased stress within the contact 29 will cause the spring 26 to throw to open circuit position. 7

When the casing I0 is hot, the spring'26 will become less convex and will movethe armature and rod assembly downwardly, relieving the stresses in the spring 26 which are created therein by the engagement of the spring with the fixed contacts, with the net result that the heating effect of the pre-established overload condition will, cumulatively with the strains created within the contact 29 due to its temperature rise resulting from the hot casing, cause the desired-inversion of the contact member 29 within the range of the overload operation desired.

The relative strengths of the snap spring 2'6- and the contact member 29 are such that reactive forces in the contact 29 during its inversion from concave to convex form, will not throw the snap spring 26 from convex to concave position. Also, the elements are so arranged that the contacts 39 of contact member 29 engage with the'fixed contacts I2 prior to the attainment of full inverting throw of the snap spring 26, so that said spring 26 resiliently urges the contacts 90 against contacts l2 with a continuing pressure, insuring a continuous pressure electrical connection therebetween.

The snap spring 26 is the primary motive force in the opening or closing of the circuit breaker under normal conditions, i. e., conditions not involving an overload in the load circuit. The solenoid coils l4, l5, perform the function of initiating the movement of the armature 2| to cause the snap spring 26 to throw, i. e., invert from one to the other of its two positions of equilibrium.

Obviously, the contact member 29 will invert only as a result of its closed circuit position. When it inverts to open circuit position, it will remain in such position because it is a double equilibrium point snap spring; and therefore when the contact member 29 cools, in open circuit position, it will remain in open position; To re-close the circuit, the operator must move the switch S to oif" position, energizing the solenoid i5 to draw the armature system downwardly. As the armature moves downwardly, the rim of the contact member 29 strikes against the dished solenoid shell l6 and inverts into its concave or closed circuit position, in which position, however, the contacts 30 of contact spring 26 remain out of engagement with the contacts 12, and may be brought into engagement therewith, only by energizing the on solenoid coil N. If the overload condition in the controlled circuit persists, the movable contact member 29 will again invert and the circuit will again be opened. It is therefore impossible to maintain a closed circuit so long as an overload condition exists.

. Such a circuit breaker is what is known in the i of temperature change to which it might be exposed in use. A maximum range of movement approximately that shown in Fig. 1 for the snap spring 26 provides satisfactory temperature compensation. Bimetallic material is now so standardized that there is no difiiculty in obtaining desired combinations from commercial sources.

From the above it will be apparent that the invention generically comprises an electrical circuit breaker which is automatically protected against overload, effected by the provision of thermostatic means, preferably of disk spring construction, which is responsive to the current of the load circuit; such thermostatic means controlling the contact means of the circuit breaker per se, combined with suitable thermostatic be made provided they do not depart from the scope of the claims.

I claim: 1. In an electric circuit breaker, the combination of contacts arranged to be connected with a 'load circuit; movable contact structure arranged to cooperate with said load circuit contacts to close and open the load-circuit, said movable contact structure including thermostatic element responsive to a predetermined overload condition in the load circuit to withdraw said movable contact structure. relative to said load circuit contacts to thereby open the load circuit; and ambient temperature responsive means controlling said movable contact structure, said ambient temperature responsive means including thermostatic means and means connecting said thermostatic means with said thermostatic element, said ther mostatic means being constructed and arranged to move said movable contact structure toward its load circuit-closing position as the ambient temperature decreases. 4

2. An electric circuit breaker as defined 1!! claim 1, in which said ambient temperature responsive means is enclosed in a housing enclosing also said movable contact structure.

3. An electric circuit breaker, as defined by claim 1, in which said thermostatic element oi the movable contact structure is a snap-.disk spring having two positions of stable equilibrium.

4. An electric circuit breaker, as defined by claim 1, in which said thermostatic means of said ambient temperature responsive means is a snap disk spring having two positions of stable equilibrium. I

5. An electric circuit breaker, as defined by claim 1, in which said thermostatic element of said movable contact structure and said thermo- :6 static means of said' bient temperature responsive means are snap disc springs having two positions oi stable equilibrium.

' WILLIAM E. STILWELL, Ja.

REFERENCES crrnn The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 1,855,967 Matthews Jan. 10, 1928 1,897,316 Marshall Feb. 14, 1933 2,057,380 Keefe Oct. 13, 1936 2,203,558 Wilson June 4, 1940 2,207,422 Vaughan et a1. July 9, 1940 2,309,207 Newton Jan. 26, 1048 2,335,880 Btilweli, Jr Dec. 7, 1943 

